It is known that with the help of femtosecond laser radiation, non-linear interactions and, at higher pulse energies or energy densities, a photodisruption in particularly optical materials or tissue can be generated.
In everyday clinical life, for example, this is utilized in eye-surgical lasers such as the “Visumax” from Carl Zeiss Meditec AG.
Here the laser system is provided with an fs laser beam source, the pulse energy of which is adjusted beforehand at a predetermined repetition rate (e.g. 500 kHz) of the laser pulses in a relevant range of, e.g. 50 nJ-5 μJ in order to always reliably generate a photodisruption in the tissue. With regard to a treatment of the cornea of the eye, the variance of the tissue properties of the individual patients is relatively low, and therefore a pulse energy of, e.g. 0.5 or 1 μJ will most certainly lead to a disruption.
However, for the treatment of a human crystalline lens aged due to presbyopia or cataract, it can be determined visually that the scattering and/or absorption properties vary from good transparency to complete opacity. Accordingly, the pulse energy value required for the photodisruptive treatment is doubtful and uncertain.
Therefore, the threshold energy for generating photodisruptions in the lens is locally subject to great fluctuations and as a result, only unsatisfactory treatment results can be achieved with a specified energy.
EP 1 663 087 discloses such an fs-laser system for treating the crystalline lens and cites a pulse energy in the range from 1 pJ to 500 nJ, i.e. a range of more than 5 magnitudes. No additional specifics are provided.
Alternatively, the overall energy applied in the eye should be as low as possible in order to safely avoid unwanted side effects, such as damage to the retina.
WO 2008/017428 by the applicant, the entire content of which is hereby incorporated by reference, describes a laser phaco system having an fs laser and a detector for acquiring the geometry of the crystalline lens in order to ensure a precise navigation within the lens. Among others, the following detector for acquiring the geometry are cited: Devices on the basis of optical coherence tomography (OCT), rotating slit Scheimpflug cameras, confocal laser scanners, and ultrasonographs. A further analysis of the tissue to be treated is not disclosed.